A spinning frame of this type is known from the European patent EP 0 462 467. The clamping device below the cop at the spindle enables it to operate with a comparatively short length of yarn for the underwinding. It is the aim to operate with an underwinding yarn length (clamping length) corresponding with a partial loop of the spindle at the height of the underwinding crown or the clamping device respectively. In order to reach this target it is necessary to determine the wound yarn length as exactly as possible. The supply quantity of yarn from the drafting unit is measured starting from the point of time at which the ring rail with the traveler has laid the yarn at a height below the upper edge of the underwinding crown. Such a device is described in detail in the European patent EP 0 528 752. The objects of the two mentioned European patents are thus considered as an integrated part of the invention being described hereafter.
From the European patent 0 480 357 it is known to control the number of revolutions of the spindles or of the drafting unit respectively individually, during the spinning out process, where however the particular problem of the underwinding with a clamping device is not being considered.
In ring spinning frames according to the known art, which are provided with electromotive drives for a fast lowering of the ring rail, the ring rail is basically moved downward at constant speed for the formation of the reverse winding. In a ring spinning frame of the present type, with a clamping device for the yarn in the underwinding position, the individual operating parameters have to be adapted to one another more exactly than in today""s conventional spinning frames. It may be necessary to specifically influence the yarn characteristics, especially during the last phase of the spin out, in order to assure an operation without disturbances. These are requirements to be met with the present invention.
Objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned from practice of the invention.
According to the invention, a spinning frame with a drafting unit, a spindle and a ring rail are provided. The drafting unit, the spindle and the ring rail are kept in coordinated operation via the respective drives, and with a clamping device for the yarn in a position below the cop on the spindle. During the formation of the reverse winding, when the yarn is led from the uppermost position on the cop into the position below the cop to the clamping device, the individual components of the drafting unit drive and of the spindle drive are being driven. They are driven in such a way that before the lower part of the cop is reached, within the second phase of the downward movement of the ring rail, the twist of the yarn is specifically being altered in order to achieve a higher strength. This occurs before the yarn is brought into the section of the clamping device and the spinning frame is decelerated to a standstill. The ring rail remains only during approximately two revolutions of the spindle in the lowest position at the clamping device, preferably however only as long until the yarn has been laid over half, up to three quarters of the circumferential length within the winding zone.
During the downward movement of the ring rail, the supply speed in the drafting unit and the number of revolutions of the spindle are being reduced in such a coordinated way that the desired yarn twist and the yarn count is at first maintained and the yarn course on the cops becomes rather steep. However, a change in yarn count can also be advantageous. After depositing the underwinding the ring rail is again lifted up from the lowest position into the position above the clamping device, whereafter first the drafting unit and then the spindle drive or both at the same time are brought to a standstill. After formation of the underwinding, the drafting unit can still be kept in operation for a short period of time in order to further supply a yam length which is additionally required because of a deflection of the yarn below the drafting unit due to the upward tilting of the yarn guide. On the other hand, during a fast downward movement of the ring rail and when at the same time the reverse winding is being laid, no yarn curlings may form due to low yarn tensions within the yam section between the drafting unit and the traveller. Here, yarn tensions may not exceed a permissible value.
The spindle drive, the ring rail drive and the drafting unit drive are linked with a control unit. The control unit comprises besides the power section a memory, an input unit and a data processor. In the data processor, operating programs for the different drives are stored. Program modules for the single drives may be provided in the control unit. Further, an input device pertains to the control unit and a memory for the entered textile technological data.
Above the clamping device, shiftable along the spindle, an underwinding crown or a cutting ring respectively, is fixedly attached to the spindle. The arrangement is made in such a way that in the clamping position for the yarn, the clamping device rests on the underwinding crown. The clamping device is pressed upwards by a spring from the lower part of the spindle and by means of a separate actuating device. Alternatively, it is pressed directly by the ring rail. During its movement, the clamping device can be shifted into the lowest downward position, that is into the opening position.
The indications for direction relate to the schematic illustration in FIG. 2. The indications for directions are not absolute but are chosen from the viewpoint of the observer. Textile technological data is entered into the input unit, such as the twist of the yarn, the mass of the cop, the cop diameter, the length of the sleeve and the ring diameter. Furthermore, maximum deceleration values for the spindle and maximal values for the ring rail speed during the downward movement within the last phase can be defined. With the help of the data processor, the operating programs for the drafting unit drive, the spindle drive and the ring rail drive are then calculated or stored in the memory respectively. Advantageously, also stored is the desired altered yarn characteristics during the last phase of the spin out.
Depending on the yarn to be produced, different parameters result for the calculation of the operating programs which can be stored as data sets in the memory. The control unit calculates the data of the operating program in a way that due to the observation of the textile technological boundary values, during the last phase of cop formation, as few thread breaks as possible occur. This happens during doffing or cop exchange respectively, and during the start of newly spinning of a cop.
Due to the clamping of the yarn below the cop, when an additional need of thread length arises, the traveller on the ring of the ring rail cannot be turned backward. Therefore, it is important that the drafting unit still supplies an additional yarn length after the yarn is already blocked in the clamping device. With this arrangement, an unthreading of the yarn from the traveller is practically impossible. While the reverse winding is performed on the cop, the deceleration of the number of revolutions of the spindle occurs with a delay value of preferably between 15 and 25 1/S2. If the yarn count is also to be maintained during this last phase of cop formation, then due to the yarn count and the yarn twist, the drafting unit deceleration has to be calculated depending on the delay in the spindle drive. The ring rail speed in consequence is to be adapted to the supply speed of the yarn, so that the yarn supply during winding of the reverse winding is just sufficient.
Besides a calculation of the operating program for the drafting unit and the ring rail, single values for the supply quantity of the yarn from the drafting unit and the lifting height of the ring rail in dependence on the numbers of revolutions on the spindle can be determined experimentally. Depending on yarn count, a ring rail speed of between 30 and 120 mm/sec is preferred. The first value stands for a fine yarn count and the second for course yarns. It is also advantageous to alter the yarn count starting at least from the point of time of performing the reverse winding in a way that a favourable condition results for inserting the yarn into the clamping device.